The development of a safe and effective HIV vaccine remains the best hope for containing the continuing spread of the AIDS epidemic. Yet, fundamental biological and practical challenges have long frustrated realization of this goal. HIV establishes a chronic infection that destroys essential immune effector functions and cannot be cleared by natural immune responses. As such, HIV infection is fundamentally different from any infectious disease that can currently by prevented by vaccination. However, recent insights into central virological and immunologic aspects of HIV disease have enabled new, more rigorous approaches for the study and development of novel HIV vaccine strategies. This Keystone Symposium is intended to foster communication of the most current results from basic and applied HIV vaccine research efforts, to identify and productively address major remaining obstacles to vaccine development, and to stimulate accelerated and increasingly effective research on HIV vaccines. The conference will be held concurrently with the Keystone Symposium "AIDS Pathogenesis" and joint sessions will be held on topics of interest to both groups. Through a comprehensive, multi- disciplinary series of research presentations, workshops and panel discussions, meeting participants will become familiar with state-of-the- art research efforts in HIV vaccine development and testing. It is anticipated that this meeting will be particularly useful for young investigators in training as they represent the next generation of HIV vaccine researchers. The better they understand the diverse biological and practical complexities that make HIV vaccine development so challenging the better able they will be able to make essential contributions to overcome these substantive obstacles.